Effect of oil flushing with nitrogen on the quality and oxidative stability of coldpressed rapeseed and sunflower oils.

BACKGROUND Oxidative stability means resistance to oxidation during purchase, processing and storage and is a key quality indicator of edible fats. Oils ought to be stored in dark-glass bottles, at low temperatures  and with no access of light in order to effectively preserve their oxidative stability. Since all vegetable oils contain unsaturated fatty acids that can react with oxygen and deteriorate over time, displacement of oxygen with inert gases may result in a reduction of the rate of oxidation. In the study the effect of oil flushing with nitrogen on the quality and oxidative stability of cold-pressed rapeseed and sunflower oils was determinate. METHODS Commercial samples of cold-pressed rapeseed and sunflower oils were stabilized by generating anaerobic atmosphere in the bottles by blowing through with nitrogen and generation of a "nitrogen cushion". Oils were tested in accelerated at 63°C and long-term at 20°C storage tests. RESULTS After 20 days of Schaal oven test, the peroxide value in the flushing with nitrogen rapeseed and sunflower oils was, respectively, 4 and 7 times lower than in the control samples (without nitrogen). In turn, of the long-term storage test (with access of light 20°C), the peroxide value of oil flushing with nitrogen after 6 months of storage was 2.3 to 2.8-fold lower, respectively, than in the control sample. In the oil samples flushed with nitrogen peroxide formation was inhibited, however, as a result of the breakdown of the peroxides already existed in the oil, gradual decrease of the oxidative stability (determined via Rancimat test) was observed along with prolonged storage of oils. CONCLUSIONS Oil flushing with nitrogen was a very effective way to reduce the changes caused by oxidation in cold-pressed rapeseed and sunflower oil.